Apparatuses for electrostatically spraying a coating product make it possible to electrostatically charge a coating product and offer a good transfer rate of the coating product onto the support to be covered.
One recurring issue in apparatuses for electrostatically spraying a coating product is controlling the start-up of the electrostatic high voltage, and therefore controlling a generator for supplying power to a high-voltage unit comprised in a sprayer, the sprayer being comprised in the apparatus.
In the field of spraying a coating product using an electrostatic sprayer, it is known to install, on a spraying air flow pipe of the sprayer, a pneumatic switch, more frequently called “flow rate contact”, which closes an electric contact when it detects a sufficient air flow rate. The closing of the electric contact makes it possible to supply power to a high-voltage unit. Such a flow rate contact has a relatively long response time, a significant bulk and weight, and a high remanence. Its operation is not very reliable when the air flow rate is low. This means that the triggering point for the high voltage is more or less precise, in particular due to the response time and remanence of the sensor.
It is also known from U.S. Pat. No. 4,441,656 to control a generator for supplying power to a high-voltage unit owing to the position of one end of a trigger actuated by an operator. This approach makes possible to ensure that the high voltage is triggered only when the trigger is actuated. This material does not make it possible to account for any defects in the air supply of a sprayer in which spraying air is used. Furthermore, this device is cumbersome, heavy and expensive.
It is also known to produce a sprayer for which the action on a trigger opens an air leak in the sprayer, that leak being protected by one or two pressure sensors mounted in differential that make it possible, when such an air leak is detected, to trigger a generator for supplying power to a high-voltage unit. The problem created by the use of an air leak on a sprayer is a needless consumption of compressed air, which quite often a source of bother for the operator, and the establishment of complex pneumatic circuits that withstand temporary overloads poorly, which is a source of breakdowns and malfunctions. Furthermore, in this type of system, time drift phenomena are commonly observed in the detection threshold of the pressure sensors. This means that the high-voltage unit is no longer reliably triggered, resulting in significant excess product consumption and additional risks for the safety of people and property.
Furthermore, it is known from FR-A-2,578,450 to use a first magnetic sensor actuated by a permanent magnet positioned in a variable position on a gun body and a second sensor used as a switch and which makes it possible to deliberately cut the generation of a high voltage by a high-voltage unit, so as to facilitate the coating of hollow bodies. This type of device implies that the sensors must be able to cut an alternating voltage varying from 20 to 35 kHz with an intensity of at least 1 A and a peak voltage of approximately 80 to 100 Volts. Indeed, once the sensors are actuated, they directly cut the electricity supply of the high-voltage unit by closing or cutting the electricity circuit of the primary of the transformer. Then, during the use of this type of apparatus, the operator presses and releases a trigger of a sprayer between 6 and 12 times per minute. The first sensor is therefore considerably biased. These stresses lead to using sensors with dimensions that are practically incompatible with their insertion inside a gun for electrostatically spraying a coating product, and even using large sensors, their lifespan is greatly reduced in such a device, due to the high voltage and current levels that they must cut.
Also known from JP-A-2004 26 7960 is an electrostatic spraying apparatus that comprises a module for controlling the current delivered to a high-voltage unit, as a function of a specific parameter inherent to an air valve of the sprayer. However, in such an apparatus, the control module directly cuts the current and voltage delivered to the high-voltage unit by the control module, which creates problems in terms of lifespan and sizing of the control module and any member for measuring a specific parameter.
The invention more particularly aims to resolve these drawbacks by proposing an apparatus for electrostatically spraying a coating product that allows a reliable and precise control of a power supply generator of a high-voltage unit, without having to detect the consumption of a fluid, such as air or coating product.